<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .active
        {
            background-color:red;
        }
    </style>
</head>
<body>
    <h1>hello,world</h1>
    <h1>hello,world</h1>
    <h1>hello,world</h1>
    <h1>hello,world</h1>
    <h1>hello,world</h1>
    <script>
        let h1List=document.querySelectorAll("h1");
        for(let i in h1List)
        {
            h1List[i].onclick=function(){
                
                if(this.className==="active"){
                    this.className="";
                }
                else{
                    this.className="active"
                }
            }
        }
    </script>
</body>
</html>